Copolycarbonates belong to the group of industrial thermoplastics. They have diverse uses in the electrical and electronics sector, as a housing material for lamps and in uses where particular thermal and mechanical properties are required, for example hair driers, uses in the automobile sector, coverings of plastic, diffusing screens or light conductor elements and lamp coverings or lamp holders (bezels).
Good thermal and mechanical properties, such as Vicat temperature (heat distortion temperature) and glass transition temperature, are practically always necessarily required for these uses. In order to achieve the increased heat distortion temperature, specific bisphenols, which have an involved synthesis and are therefore also expensive, must be resorted to.
It is known that in the case of polymers these properties depend on the molecular weight. Generally, they increase with increasing molecular weight and approach a limit value. In this context, however, not only the molecular weight per se, but the molecular inhomogeneity factor U=(Mw/Mn)−1 is of importance. Large inhomogeneity factors can cause negative thermal and mechanical properties in copolycarbonates. The molecular weight furthermore has a direct influence on the viscosity (solution and melt viscosity) and therefore on the flowability of a polymer melt at a given processing temperature. However, high molecular weight products flow more poorly and can therefore be processed only with significantly shorter cycle times. This route is therefore not feasible for also fulfilling the necessary mechanical properties and heat distortion temperature at a relatively low molecular weight. Moreover, it is known, that low molecular weight compounds and oligomers can have a negative impact on thermal and mechanical properties of copolycarbonates.
Alkylphenols, in particular p-tert-butylphenol (also referred to hereinafter as “BUP” for simplification), as chain terminators for the preparation of polycarbonate are known (see, e.g., International Pat. Pub. No. WO 01/51541, European Pat. Pub. No. EP 1249463A and International Pat. Pub. No. WO 2004/063249, the entire contents of each of which is hereby incorporated herein by reference). However, the publications cited describe neither polycarbonates having a defined molecular weight distribution nor the use of alkylphenols for the preparation of copolycarbonates having a defined molecular weight distribution. In particular, no indication of the influence of the chain terminator on the molecular inhomogeneity factor in a given copolymer composition when phenol is used as the chain terminator nor on the Vicat temperature is to be found.